1. Field of the Invention
The present invention relates to an ink jet recording head for recording on a recording medium by discharging ink, an ink jet recording apparatus, and a method of manufacturing the ink jet recording head.
2. Description of the Related Art
A basic performance of an ink jet printer largely depends on its image quality and high speed performance. In order to improve the image quality, it is necessary to reduce ink droplets in size as small as possible, and desirably set the size thereof to about 1 pl or less, which is above a visible limit, on a paper surface. On the other hand, in order to obtain the high speed performance, it is necessary to increase an amount of ink applied to a medium within a predetermined period of time. In order to accomplish this by using small-size liquid droplets, it is necessary to increase density of each recording element and increase a response frequency, which has limitations in terms of structure and fluid. As a method of solving the problem, U.S. Pat. No. 5,208,605 proposes a technique of providing multiple discharge ports for discharging different sizes of liquid droplets to one recording head.
Further, U.S. Pat. No. 5,478,606, for example, discloses a method of forming such a fine discharge port and an ink flow path having high density. U.S. Pat. No. 5,478,606 proposes a method of forming a flow path such that the ink flow path is formed by using a photosensitive resin, another photosensitive resin is applied thereonto and dried to form a discharge port, and then the first photosensitive resin is removed. According to the method, both the flow path and the discharge port are formed by exposure, so it is possible to process them finely and with high density.
With regard to the ink jet recording head having multiple sizes of liquid droplets as described above, it is more advantageous for obtainment of higher density to arrange an array of nozzles for discharging small liquid droplets separately from an array of nozzles for discharging large liquid droplets. In order to pursue the higher density of each nozzle, it is most advantageous to arrange the nozzles for small liquid droplets in a staggered manner with density twice as much as that of the nozzles for large liquid droplets.
However, when another resin is applied onto the resin formed in a shape of an ink flow path, a thickness of the resin is not completely uniform, and the thickness has variation due to effects such as viscosity of the resin, surface tension, and solid content density. A portion of the ink flow path with higher density has a wider area for the flow path, so the thickness of the resin of the flow path member formed on the corresponding portion becomes thicker than the other portions for large liquid droplets. As a result, the discharge resistance is increased and the discharge efficiency is lowered, and thus a discharge failure is liable to occur.
FIGS. 8A to 8C are plan views and cross-sectional diagrams taken along the line A-A of a conventional recording head.
In the prior art, a distance Lb between one end of a flow path 510 for discharging small liquid droplets and the other end thereof is 360 μm, and recording elements 506 are arranged in a staggered manner at 1200 dpi (interval of 21 μm). On the other hand, a distance La between one end of a flow path 510 for discharging large liquid droplets and the other end thereof is 280 μm, and recording elements 506 are arranged in a staggered manner at 600 dpi (interval of 42 μm). Thus, the distance La of the flow path for large liquid droplets is 280 μm, and the distance Lb of the flow path for small liquid droplets in which an arrangement density of the recording elements 506 is high is 360 μm, which is about 1.3 times as long as the distance La. The recording head includes driving circuits 521, a substrate 523, and a flow path resin 525.
Therefore, according to the prior art, a flow path member 508 has a difference dh in thickness which is 2 μm at maximum. This indicates that a difference in resistance of 20% is generated when it is assumed that a thickness of the discharge port portion is 10 μm, and some effects are shown, for example, deviation of each placement position of small liquid droplets and large liquid droplets on a paper surface due to a difference between discharge speeds thereof, especially at the time of recording of a high resolution image.
On the other hand, in a case of optimizing the thickness of the resin so as to discharge small liquid droplets, the thickness of the resin corresponding to the portion of the flow path for large liquid droplets is reduced, with the result that deformation or the like of the resin due to strength degradation is liable to occur.